1. Field of the Invention
The present invention relates to a stator manufacturing apparatus and a stator manufacturing method for rotary electric machines, and in particular, to a stator manufacturing apparatus and a stator manufacturing method for rotary electric machines, with which the segment cores of a stator to be manufactured are shrink-fitted to an outer cylinder, in manufacturing the stator for a rotary electric machine.
2. Description of the Related Art
In recent years, small size, high power and high quality have been demanded of rotary electric machines used as electric motors and electric generators. Taking rotary electric machines loaded on vehicles as an example, the space for loading such a rotary electric machine has been reduced more and more, while the output has been required to be more enhanced.
Rotary electric machines that have been known include one which is provided with a stator having a stator coil formed of continuous windings, as disclosed in Japanese Patent No. 3894004. In the stator of such a rotary electric machine, twelve wires are used to form a three-phase winding of the stator coil. Accordingly, the stator has a structure in which twenty-four wire ends are axially projected from an axial end face of the stator core. Therefore, this type of stator requires a large space outside the axial end face of the stator core, so that the wire ends can be connected with each other. This however has raised a problem of increasing the axial dimension of stators.
To counter this problem, it has been considered to suppress the size of a stator by reducing the size of the stator coil.
Meanwhile, as an example of a method for manufacturing stators consisting of continuous windings, the following method has been known. In the method, a plurality of shaped wires are produced, first, from electrically conductive wires in each of which a plurality of straight portions are juxtaposed being connected with each other via turn portions. Then, these shaped wires are integrated to form an integrated body. In the integrated body, one shaped wire is paired with another shaped wire, and a plurality of such shaped-wire pairs are juxtaposed in the longitudinal direction of the integrated body. In each of the shaped-wire pairs composing the integrated body, the plurality of straight portions of one shaped wire are superposed on the respective plurality of straight portions of the other shaped wire to form a plurality of straight superposition portions in the longitudinal direction of the integrated body.
In this way, the plurality of straight superposition portions are juxtaposed in the longitudinal direction of the integrated body. The integrated body is then wound about a core member with a predetermined number of turns to thereby form a wound body. In the wound body, the plurality of straight superposition portions in each shaped-wire pair are radially stacked to form a plurality of straight stack portions in the circumferential direction. The wound body obtained in this way is used as a cylindrical cage-shaped stator coil. In assembling this stator coil into a stator core, each of the straight stack portions are disposed in respective slots of the stator core, while the turn portions are disposed outside the slots.
However, it is quite difficult to assemble such a cylindrical cage-shaped stator coil into an integral type stator core already having a shape of a core. To counter this, segment cores are used, each having a shape resulting from circumferentially dividing an annular core into a plurality of pieces. Use of such segment cores permits the segment cores to be individually assembled into the cylindrical cage-shaped stator coil from outside, and then to fit the entirety into an outer cylinder, for manufacturing a stator. The fitting into the outer cylinder is performed by using a so-called shrinkage fitting method.
In performing the shrinkage fitting, the stator core, in which a plurality of segment cores are circumferentially disposed, is required to be evenly shrunk in the radial direction from the side of the outer circumference. Otherwise, the stator core will be distorted and thus the circularity (e.g., 0.05 mm) required for a rotary electric machine cannot be ensured. Since the stator core in fact has been divided along the circumference, it is difficult to evenly shrink the stator core. Thus, segment cores have created a problem of difficulty in achieving shrinkage fitting with a uniform diameter throughout the stator core.